Acrylic pressure sensitive adhesives with controlled humidity response

Abstract

A pressure-sensitive adhesive composition includes from about 30 weight percent to about 70 weight percent solids in an aqueous medium. The solids include an acrylic polymer having a glass transition temperature of from about -25° C. to about -85° C. and having an acid number of from about 3 to about 30 and from about 0.75 parts by weight to about 5 parts by weight of a humectant per 100 parts polymer.

I claim: 
     
       1. A pressure sensitive adhesive composition, consisting of from about 30 weight percent to about 70 weight percent solids in aqueous medium, said solids comprising an acrylic polymer dispersed in an aqueous medium, said polymer having a glass transition temperature of from about -25° C. to about -85° C. and an acid number of from about 3 to about 30; and from 1 part by weight to about 2 parts by weight per 100 parts polymer of a non-volatile humectant dissolved in the aqueous medium, provided that the humectant is not urea. 
     
     
       2. The composition of claim 1, wherein the humectant is a polyol, a sugar, a protein-based humectant or a mixture thereof. 
     
     
       3. The composition of claim 1, wherein the humectant is selected from the group consisting of glycerol, polyethylene glycols having a molecular weight of from about 100 to about 1000 and mixtures thereof. 
     
     
       4. The composition of claim 1, wherein the polymer comprises repeating units derived from a (C 1  -C 20 )alkyl (meth)acrylate monomer. 
     
     
       5. The composition of claim 4, wherein (C 1  -C 20 )alkyl (meth)acrylate monomer is selected from the group consisting of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cetyl acrylate, stearyl acrylate, eicosyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isodecyl methacrylate, lauryl methacrylate, cetyl methacrylate, stearyl methacrylate, eicosyl methacrylate and mixtures thereof. 
     
     
       6. The composition of claim 1, wherein the polymer further comprises repeating units derived from a monoethylenically unsaturated carboxylic acid monomer. 
     
     
       7. The composition of claim 6, wherein the monoethylenically unsaturated carboxylic acid monomer is selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonoic acid, fumaric acid and mixtures thereof. 
     
     
       8. The composition of claim 1, wherein the polymer has a glass transition temperature of from about -30° C. to about -65° C. 
     
     
       9. The composition of claim 1, wherein the humectant is selected from the group consisting of 1,3-butane diol, 1,2,6-hexanetriol, trimethylol propane, pentaerythritol, glycerol, polyethylene glycols having a molecular weight of from about 100 to about 4000, poly(ethylene oxide/propylene oxide) copolymers, sorbitol, glucose, sucrose, corn syrup, ethoxylated (10-40 moles ethylene oxide) glycerol, ethoxylated (10-40 moles ethylene oxide) glucose, propoxylated (10-40 moles propylene oxide) glucose, hydrolyzed soy protein, soluble collagen and mixtures thereof. 
     
     
       10. A pressure sensitive adhesive composition, consisting of from about 30 weight percent to about 70 weight percent solids in aqueous medium, said solids comprising an acrylic polymer dispersed in an aqueous medium, said polymer having a glass transition temperature of from about -25° C. to about -85° C. and an acid number of from about 3 to about 30; and from 1 part by weight to about 2 parts by weight per 100 parts polymer of a non-volatile humectant dissolved in the aqueous medium, said composition being relatively insensitive to the relative humidity of the environment.